Roll apparatus



April 14, 1970 R. MOSER 3,505,716

ROLL APPARATUS Filed Dec. 1l. 1967 PRIOR ART D F/G.

#3 38 5, ,BTO (3/ 36 37 35 36 37 38 4/ el Al 4f 3f F/G. 2 L3 INVENTOR. RABIN MOSER lBY A M-Jw Afro/Mfrs United States Patent O 3,505,716 ROLL APPARATUS Rabin Moser, Fairport, N.Y., assigner to Xerox Corporation, Rochester, NY., a corporation of New York Filed Dec. 11, 1967, Ser. No. 689,557 Int. Cl. Bill 13/02 U.S. Cl. 29-116 1 Claim ABSTRACT OF THE DISCLSURE A roll apparatus for applying pressure uniformly across the entire length of the operating surface or nip defining line of pressure rolls. The apparatus comprises a roll shell supported by bearings on a shaft which is internally stressed to counteract the bending moments applied to the shell.

This invention relates to roll structures and, more particularly, to apparatus for applying pressure uniformly across the operating surface or nip dening line of pressure rolls.

Pressure rolls are commonly used in a number of arts, such as, making of paper, coating of paper or fabrics, and calendering of webs made from paper, plastic and thin sheets of metal. Also, in the art of copying, pressure rolls are used for transferring an image onto copy sheet and/ or as a fixing device to affix the image permanently to its support sheet. Normally a web or sheet is passed through a nip formed between a pair of superimposed rolls which are subjected to pressure. The pressure applied at the mp tends to load both the lower roll to deflect it centrally and downwardly and to the upper roll to deflect it centrally and upwardly. Such deflection results in the nonuniform application of forces across the nip especially 1n the case of where the length to diameter ratio is large.

It is common practice to correct such deflection by crowning one or both of the pressure rolls. It has been found, however, that crowning of a roll causes speed differentials between the middle and sides which tend to wrinkle the web or sheet as well as other undesirable operating features. Also, crowning requires accurate -and expensive finishing of the roll surface to obtain the desired diameters along the length of the roll. Moreover, such crowning is carried out on the basis of a predetermined set of force conditions which would not be satisfactory under a different set of force conditions. For these and other reasons, crowning of rolls has not proven entirely satisfactory as a way to apply pressure uniformly across the entire length of the operating surface of the pressure rolls.

In accordance with the present invention, a uniform pressure is applied across the nip of pressure rolls irrespective of load conditions and Without the above noted disadvantages of a crown shape.

It is therefore an object of the present invention to 1mprove pressure roll structures.

It is another object of the present invention to apply pressure uniformly along the entire length of the operating surface or nip defining line of pressure rolls.

It is another object of the present invention to maintain substantially uniform pressure in the nip formed by superimposed pressure rolls under varying load conditions.

It is still another object of the invention to provide roll apparatus in which force couples internally applied counteract external load stresses.

It is still a further object of the present invention to apply uniform lpressure along the operating surface of a roll without subjecting the roll to stress reversals thereby eliminating fatigue.

The foregoing objects and others are accomplished, generally speaking, by mounting a roll shell supported rice by bearings on a shaft which is internally stressed by force couples to counteract bending moments applied to the shell.

For a better understanding of the persent invention, as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in conjunction with the accompanying drawing, wherein:

FIG. 1 is a diagrammatic illustration of a pair of pressure rolls illustrating in somewhat exaggerated form the manner in which rolls of the prior art are deflected.

FIG. 2 is an elevational view of a roll assembly constructed in accordance with the present invention, parts thereby being shown in section and other parts diagrammatically;

FIG. 3 is a sectional view of the roll assembly of the invention taken along lines 3-3 of FIG. 2; and

FIG. 4 is an isometric view of the shaft member of the roll assembly.

Referring iirst to FIG. l, there is shown a pressure roll assembly of the prior art indicated generally by reference numeral 10 and comprising a roll 11 at the bottom mounted on suitable bearings 12 and 13 which are secured to a fixed mounting F. Immediately above roll 11 is another roll 14 which, in turn, is mounted for rotation in bearings 15 and 16. Roll 11 is provided with a left hand stub shaft 11a which is rotatably received by left hand bearing 12 and a right hand stub shaft 11b which is rotatably received by right hand bearing 13. In similar fashion roll 14 is provided with a left hand stub shaft 14a rotatably received by left hand bearing 15 and a right hand stub shaft 14h rotatably received by right hand bearing 16.

As will be noted the oentroidal axis 20 of roll 11 is deflected downwardly below horizontal or center line 21 at the middle of the roll. The reason for this is that a load is being applied to roll 11 by roll 14. This load is transmitted through a sheet or web 23 which is shown in exaggerated thickness passing through the nip formed between rolls 11 and 14. The central portion of the top surface of roll 11 is crowned so as to extend a distance R above the outer extremities of the roll and the bottom surface of roll 11 is downwardly bowed still a greater distance D due to the pressure on the roll. The amount of operating crown R depends upon the amount of original crown formed on roll 11 and the load of roll 14 mounted thereabove. As will be appreciated, if it is desired to operate pressure roll assembly 10 with substantially no operating crown in roll 11, the initial crown and total load of roll 14 must be correlated to obtain the desired operating flatness at the nip. It will be further appreciated, however, that to machine a crown shape to exact dimensions along the entire length of the roll is difiicult and costly. Also if it becomes desirable to vary pressure loads, then a different crown shape is necessary since a fixed crown operating under different load conditions results in non-uniform pressure distribution at the portion of the web passing through the nip causing wrinkling and other undesirable operating conditions.

Referring now to FIGS. 2 4, there is shown and generally designated by numeral 30, a roll assembly according to the present invention. Roll assembly 30 comprises a cylindrical shell 31 rotatably supported on ball bearings 33 received between inner and outer races 35 and 36, respectively. Outer races 36 are separated by spacer elements 37 and are prevented from movement along sleeve 31 by snap rings 38. Received concentrically Within shell 31 and ibearings 33 is a shaft member 40 is selectively stressed to counteract external forces acting on cylindrical shell 31 as will become more apparent. Shaft member 40 is non-rotatably fixed on a support 41 by set screws 43. It should be understood that bearings 33 need not be the same in number 0r construction as shown, and it is only intended that suitable bearings be positioned along shaft member 40 essentially in the locations indicated.

In accordance with the present invention, shaft member 40 is adapted for bowing or bending to counteract forces tending to deflect shell 31 under load conditions. To accomplish the desired bending of the shaft member 40, it is bored eccentrically to receive a tensioning member S1 which extends beyond the ends of the shaft member and shell 31. Tensioning member 51 is formed with threaded portions 52 on the ends which receive internally threaded nut members 53. By moving nut members 53 along the tensioning member 51 toward shaft member 40, compression forces are established along an axis parallel to the axis of the shaft member 40. This causes the shaft member to become internally stressed and bow in a direction to oppose external forces tending to deflect shell 31. Desirably shaft member 40 is formed with tubular openings 56 at the ends and a rectangular channel 57 along the central portion of the shaft member. It should be understood, however, that either a tubular opening or recitangular channel could be formed along the entire length of the shaft member, as desired. Thus, any suitable crosssection can be utilized for the hollow portion of shaft member 40, since the geometrical shape of the opening does not affect the function of the shaft member appreciably.

To facilitate bending shaft member 40 there is formed therein a series of slots 58 which are uniformly spaced and which extend progressively longer in depth as they approach the center of the shaft member where the external bending moment is greatest. The minimum crosssectional areas of the shaft member should be suiciently great such that stress induced by tensioning member 51 will not exceed the yield strength of the material utilized for the shaft member. Generally speaking, maximum bending depends upon the magnitude of the forces applied as well as the strength of the material of the shaft member. Any suitable high strength material can be used. Typical materials are steel and titanium, as Well as ferrous and non-ferrous alloys.

It may be desirable to apply force differentials along the roll assembly 30 for different operating conditions. To this end nut members 53 may be tightened beyond a reference or normal position thereby increasing the pressure exerted on the middle of the roll assembly. On the other hand, where nut members 53 are loosened beyond a reference position, lower pressures are exerted in the middle and hence greater pressure will be exerted at the ends of the shaft member. Also, it will be appreciated that with this kind a exibility of the roll assembly continuous `adjustments can be affected during operating conditions. It should be understood that while roll assembly 30` is bowed when under no load condition it is straight in the loaded condition. Thus the surface of the roll does not alternate between a flat and crowned shape during actual working conditions as in the case of the pn'or art pressure rolls.

With the present invention it is possible to apply pressure uniformly across the entire length of the operating surface of pressure rolls without a crown shape. Thus `crown shapes, which are quite difficult and costly to obtain, are no longer required. A particular advantage of the instant invention is that when in the loaded condition, the roll surface is uniformly straight at the nip as well as any other position around the periphery of the roll. Hence. there is no flexing or stress reversal on the roll structure. This is extremely important since pressure roll assemblies are normally under great presures which cause fatigue. Also, each bearing is uniformly loaded to attain a longer operating life. Still another feature of the invention is in the sensitive control over the stressing of the roll structure which permits a highly balanced force to be exerted under various load conditions.

Although particular arrangement of the invention have been illustrated and described above, still other arrangements as would 'be apparent to those skilled in the art are intended to be included herein. Thus shaft member 40 could be formed from segmented parts instead of being a solid member.

What is claimed is:

1. Roll apparatus comprising:

a shell member,

a shaft lmember disposed in said shell member in coaxially spaced relation therewith,

said shaft member being formed with an elongated radially outwardly opened hollowed portion disposed on an axis eccentric to that of said shaft member and defined by spaced wall sections along its longitudinal extent and tubular sections at its ends,

said wall sections being formed with slots uniformly spaced and progressively longer toward the center of said shaft member,

bearing means rotatably received in said shell member between said shell member and said shaft member and uniformly distributed along the length thereof, and

force generating means including a tensioning member received by said hollowed portion for selectively -applying a force between the ends of said shaft memtber parallel to the axis of said shaft member to cause a predetermined stress thereon, whereby external forces acting on said shell member may be uniformly balanced.

References Cited WALTER A. SCHEEL, Primary Examiner L. G. MACHLIN, Assistant Examiner U.S. C1. X.R. 267--1 

